Coated metal article and method of coating

ABSTRACT

A metal article having a corrosion-resistant, adherent surfacecovering, hydrophobic, thermosetting polymer film. A method of coating a metal article to make it resistant to corrosion comprising the steps of forming a metallic chromating surface thereof, applying a hydrophobic, thermosetting polymer to a surface thereof and heating the article at a temperature of at least about 300* F. to convert the polymer into a hard, adherent film.

United States Patent 1191 Palisin, Jr.

COATED METAL ARTICLE AND METHOD OF COATING Stephen P. Palisin, Jr.,Cleveland,

Ohio

Assignee: The Empire Plating Company,

Cleveland, Ohio Filed: Nov. 18, 1971 Appl. No.: 200,224

Related US. Application Data Continuation of Ser. No. 887,397, Dec. 22,l969, abandoned.

Inventor:

[1.8. CI.'. 29/195, 204/38 E, l48/6.2l Int. Cl B23p 3/00, C23c 7/26Field of Search .1 204/38 S, 38 E, 38 R, 37;

References Cited UNITED STATES PATENTS 9/1970 Smith et al. 204/38 SModern Electroplating by Lowenheim, 1963 page 425 Primary Examiner-JohnH. Mack Assistant Examiner-R. L. Andrews Attorney, Agent, or FirmBlytheD. Watts et al.

[ ABSTRACT A metal article having a corrosion-resistant, adherentsurface-covering, hydrophobic, thermosetting polymer film.

A method -of coating a metal article to make it resistant to corrosioncomprising the steps of forming a metallic chromating surface thereof,applying a hydrophobic, thermosetting polymer to a surface thereof andheating the article at a temperature of at least about 300 F. to convertthe polymer into a hard, adherent film.

3 Claims, No Drawings of a hydrophobic, thermosetting polymer.

COATED METAL ARTICLE AND METHOD OF COATING This application is acontinuation of my pending application Ser. No. 887,397, filed Dec. 22,1969 and now abandoned.

BACKGROUND The prior art most nearly pertinent to this invention andknown to me is U. S. Pat. Nos. 3,031,333 and 3,556,869. These patentsdisclose processes which were not devised to, and would not, producearticles which would meet the severe service conditions met by articlesproduced by the present invention.

SUMMARY The present invention provides extremely corrosionresistantcoverings for, and a method of producing such coverings on, metalarticles. Such articles maybe composed of iron, steel, aluminum, zinc,bronze or copper alloys. The method consists of chromating a surface ofthe article or of a layer of metal on; the article and covering thechromated surface with a heat hardened film According to the presentinvention, metal articles when composed of aluminum, cast iron,malleable iron, steel, zinc, bronze or copper alloy are cleaned in anysuitable conventional manner, for example, by tumbling the article incaustic soda or by passing an electric current through such a solutionwith the metal article constituting the anode. After such cleaning, thearticle is rinsed in cold water, is then dipped in a dilute acidsolution, and again rinsed in cold water. When the article is composedof ferrous metal, aluminum,bronze or copper alloys, a percent sulfuricacid solution or a 25 percent hydrochloric solution is sufficient toneutralize the caustic soda. When the article is composed of zinc, avery weak acid solution is used.

In certain instances where even better cleaning of a ferrous metalarticle is desired or where its surface is to be activated, the articlemay be reversely treated in an alkaline cyanide bath, i.e., by passing acurrent through the bath for about 30 seconds while the article is theanode in the circuit and then reversing the current flow for'about 30seconds while the article is the cathode in the circuit. Following thisreverse treatment, the article is rinsed in water if it is to be platedpromptly thereafter, or it may be rinsed in a dilute sodium cyanidesolution to prevent rusting when it is not to be plated promptly.

The thus cleaned metal article composed of iron, bronze or copper alloysis then electrolytically plated in a conventional manner, as by makingit the cathode in an electrolytic bath. Preferably cadmium or zinc isthe coating metal and either may be deposited on the article from a.conventional bath such, for example, as cadmium cyanide or zinc cyanide.Nickel and chro-. mium may also be used as coating metals. Any suitableconventional bath composition may be used for depositing either of thesemetals, for example, a nickel sulfate bath may serve for the chromiumdeposition. A current density of about 10 amperes per square foot issuitable and the plating action is continued until between about 0.0002inch to 0.005 inch layer of the base metal has been deposited on thearticle.

On aluminum, a layer of another metal such, for example, as copper maybe applied before the coating of cadmium or zinc is applied/When thearticle is com- 2 posed of zinc, a coating of cadmium, zinc, nickel orchromium is deposited on the surface thereof. After such deposition, thearticle is rinsed with water and then is rinsed in dilute aqueous nitricacid.

Following the electroplating and rinsing operations, the surface of thecoating metal, or of the article if composed of zinc, is chromated. Thischromating step consists of treating the cadmium or zinc in such amanner as to convert the metal surface thereof into a clear, stain-freefinish with corrosion While properties. Whiel various substances may beused for such chromating action, I prefer to use a chromating materialconsisting of about 90 percent trioxide and about 10 percent sodiumbisulfate dissolved inwater, the concentration of this chromatingmaterial being between about 6 oz. and about 16 oz. per gallon of water.The article to be chromated is thoroughly rinsed to free it from alkalisand is then dipped into the chromating solution for between about 10seconds and about 25 seconds. Preferably that solution should be at atemperature between about 65 and about 95 F. Upon removing the articlefrom the chromating bath, it is thoroughly rinsed with water.

The chromated surface on the metal article is then covered withhydrophobic, thermosetting polymer and the article is heated at atemperature between about Hexamethoxy methyl melamine about 15.3% EthylAcrylate about l6.0% Methacrylic Acid about l.0% Chromium Trioxide about0.1% ,Water about 67.6%

Other film-forming compositions which may be used include thehexamethoxy methyl melamine of the foregoing composition withequivalents of the other'ingre-.

dients thereof.

The above preferred film-forming composition has given new andunexpected results in terms of corrosion prevention. For example, thefilms formed by this invention had a pencil hardness of l-l-3, excellentflexibility, abrasion resistance and adhesion and evidenced nodegradation after being exposed for hours to humidity and to salt sprayconditions. In contrast therewith, films composed of epoxy solventlacquer had' a pencil hardness of H, good flexibility and abrasionresistance and fair adhesion and were affected when exposed for 100hours to humidity or to salt spray.

Films composed of nitrocellulose had a pencil hardness of H, poorflexibility and abrasion resistance, fair adhesion and were affectedwhen exposed for 25 hours to humidity or salt spray.

Having thus described this invention in such full, clear, concise andexact terms as to enable any person skilled in the art to which itpertains to make and use the same, and having set forth the best modecontemplated of carrying out this invention, I state that the subjectmatter which I regard as being my invention is particularly pointed outand distinctly claimed in what is claimed, it being understood thatequivalents or modifications of, or substitutions for, parts of theabove specifically described embodiments of the invention may be madewithout departing from the scope of the invention as set forth in whatis claimed.

What is claimed is:

l. The method of making a metal article resistant to corrosion whichcomprises the steps of electroplating, with a metal selected from thegroup of metals consisting of zinc, cadmium, nickel and chromium, asurface of an article composed of metal selected from the group ofmetals consisting of aluminum, iron, zinc, brass and copper alloys,chromating the electroplated surface by treating it for between about 15seconds and about 25 seconds with water containing between about 6 oz.and about 16 oz. per gallon of a liquid composed of about 90 percent ofCrO and about 10 percent of sodium bisulphate, rinsing the resultingchromated surface with water, covering the said chromated surface withhydrophobic thermosetting polymer and heating said article to aboveabout 300 F. to convert the polymer into a hard film.

2. A metal article composed of a metal selected from the group of metalsconsisting of aluminum, iron, brass, copper alloys and zinc, having anelectrodeposited coating on a surface thereof selected from the group ofmetals consisting of zinc, cadmium, nickel and chromium, said coatinghaving a chromated surface formed by being treated for between aboutseconds and about seconds with water containing between about 6 oz. andabout 16 oz. per gallon ofa liquid composed of about 90 percent of CrOand about 10 percent of sodium bisulphate followed by rinsing thechromated surface with water, and a film of hydrophobic thermosettingpolymer adhering to said chromated surface, which film has been hardenedby heating the article to above about 300 F.

3. A method of protecting a metallic surface to render it highlyresistant to salt spray corrosion and to abrasion, wherein the surfaceis composed of a metal selected from the group of metals consisting ofaluminum, iron, zinc, brass and copper alloys, comprising the steps of:

a. electroplating the surface with a metal selected from the group ofmetals consisting of zinc, cadmium, nickel and chromium;

b. chromating the electroplated surface to produce a clear, blemish freecolorless chromate coating thereon by treating it for between about 15seconds and about 25 seconds with water containing between about 6 oz.and about 16 oz. per gallon of a liquid composed of about,90 percent ofCrO and about 10 percent sodium bisulphate;

c. rinsing the chromated surface with water to flush away chromatingsolution remaining thereon;

d. coating the chromated surface with a transparent colorlesshydrophobic thermosetting polymer; and

e. heating the article to above about 300 F to convert the polymer to ahard, colorless transparent film thereby providing the surface with ablemish free corrosion resistant finish.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORREFJTIONPATENT NO. 3,790,355 P DATED 3 February 5, 1974 E M Stephen P. Palisin,Jr.

It is certified thai error appears in the ab0ve-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 10, after "corrosion" insert r eslstlng Signed and Sealedthis i sixteenth Day of September 1975 [SEAL] Arrest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner uflarenlsand Trademarks a I fio v UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3 ,790,I 55 Dated February 5 1974 lfiventofls)StephenP. Palisin, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 60 after "the? insert H nickel deposition and a chromicacid bath may serve for the Column 2 line 10,

WhieD should read While same line 10 cancel "While" Column 2, line 13,after the first occurrence'of the word "percent" insert 4? chromium HSigned and sealed this 17th day of September 1974.

(SEAL) Attest:

C. MARSHALL DANN GIBSON JR. i in Officer Commissioner of Patents FORMPC4050 USCOMM-DC 60376-P69 US. GOVERNMENT PRINTING OFFICE 7 I9650'35633L

2. A metal article composed of a metal selected from the group of metalsconsisting of aluminum, iron, brass, copper alloys and zinc, having anelectrodeposited coating on a surface thereof selected from the group ofmetals consisting of zinc, cadmium, nickel and chromium, said coatinghaving a chromated surface formed by being treated for between about 15seconds and about 25 seconds with water containing between about 6 oz.and about 16 oz. per gallon of a liquid composed of about 90 percent ofCrO3 and about 10 percent of sodium bisulphate followed by rinsing thechromated surface with water, and a film of hydrophobic thermosettingpolymer adhering to said chromated surface, which film has been hardenedby heating the article to above about 300* F.
 3. A method of protectinga metallic surface to render it highly resistant to salt spray corrosionand to abrasion, wherein the surface is composed of a metal selectedfrom the group of metals consisting of aluminum, iron, zinc, brass andcopper alloys, comprising the steps of: a. electroplating the surfacewith a metal selected from the group of metals consisting of zinc,cadmium, nickel and chromium; b. chromating the electroplated surface toproduce a clear, blemish free colorless chromate coating thereon bytreating it for between about 15 seconds and about 25 seconds with watercontaining between about 6 oz. and about 16 oz. per gallon of a liquidcomposed of about 90 percent of CrO3 and about 10 percent sodiumbisulphate; c. rinsing the chromated surface with water to flush awaychromating solution remaining thereon; d. coating the chromated surfacewith a transparent colorless hydrophobic thermosetting polymer; and e.heating the article to above about 300* F to convert the polymer to ahard, colorless transparent film thereby providing the surface with ablemish free corrosion resistant finish.